The present invention relates to a method by which pentose syrups can be produced in a packed bed reactor directly from hemicellulose material in such a manner that the syrups can be directly utilized for fermentation or alternatively stored without undergoing degradation.
With petroleum resources dwindling throughout the world, efforts are being made to utilize alternative sources of energy. Recently, mixtures of gasoline and alcohol have been touted as but one means of alternate energy savings. In order to provide sufficient gasohol products, an economic means for producing the necessary alcohol is needed. Heretofore, production of such alcohol has been chiefly carried out by the conversion of six-carbon sugars derived mainly from grain products and raw sugar. With the increase in cost of such six-carbon sugar materials, there is a need for alternative economic feedstocks for the production of alcohol. Many of the available hemicellulosic feedstocks which have been regarded as waste products, such as bagasse, remain untapped due to the lack of a viable economic means to convert such hemicellulosic waste materials to useful energy forms such as ethanol.
Early work relating to the acid hydrolysis of cellulosic material concentrated primarily on the production of glucose from cellulose. As described by E. C. Sherrard and F. W. Kressman (Ind. and Eng. Chem., 37, 4 (1945)) such work involved charging batch reactors with wood acidified with 2% to 4% sulfuric acid, heating with steam to 100 to 120 psi for about 30 minutes, and thereafter leaching the sugars from the residue in a diffusion battery. However, as noted by R. H. Plow, et al., Ind. and Eng. Chem., 37, 37 (1945), due to the high temperatures and pressures used, excessive degradation of the pentose sugars results.
It has been reported that pentoses can be produced at lower temperatures and pressures to yield pentoses suitable for production of acetone, furfural or alcohols such as butanol and 2,3 butylene glycol. (See W. T. Schreiber, et al., Ind. and Eng. Chem., 22, 497, (1930); and J. W. Dunning, et al., Ind. and Eng. Chem., 37, 24, (1948)).
One of the major deficiencies of these acid processes is the excess of acid which is consumed, which poses obvious disposal and environmental concerns. In addition, these processes tied together separation with reaction and are not suitable for fermenting pentoses to ethanol.
In the Noguchi-Chisso process ("The Chemical Technology of Wood," Hermann F. J. Wenzel, Academic Press, p. 157-252, 1970; and R. L. Mehlberg, "Low Liquid Hydrolysis of Corncob Hemicellulose by Hydrochloric Acid," Ph. D. Thesis, Purdue University, Aug. 2, 1979) pentoses have been removed by hydrolysis at 100.degree. to 130.degree. C. with between 3% and 5% sulfuric acid or 1% to 15% hydrochloric acid at a liquid:solids ratio between 0.5 and 3.0. It appears that the pentoses are wasted with the acid waste water.
As noted above, many of the available hemicellulosic feedstock materials have been regarded as waste products. However, due to recent advances, such as described by Chen, et al., U.S. Application Ser. No. 100,816, filed Dec. 6, 1979, technology is now available which provides for the fermentation of pentoses into ethanol--a valuable synthetic fuel. With the development of such technology, there is a continuing need to provide a viable economic means for conversion of hemicellulose and synthesis of ethanol.
One problem in the processing of any hemicellulosic material arises from the seasonal nature of the material (e.g., sugarcane bagasse and corn), thus necessitating storage of such material for year round operation. Attendant with the storage problem is the problem occasioned by rapid degradation of hemicellulosic material when exposed to the environment. Even with storage indoors at ambient temperatures, degradation will occur which renders the material less suitable for subsequent treatment in the production of alcohol.
Accordingly, it is the primary object of the present invention to provide a viable economic means by which hemicellulose can be processed in a packed bed reactor to yield a pentose syrup suitable for fermenting in the production of ethanol.
This and other objects will be more apparent from the discussion which follows.